Field
The disclosure relates to non-magnetic metal alloys with excellent wear properties for use in dynamic three-body tribological wear environments where an absence of magnetic interference is required.
Description of the Related Art
Conditions of abrasive wear can be damaging as they often involve sand, rock particles, or other extremely hard media wearing away against a surface. Applications which see severe abrasive wear in the prior art typically utilize materials of high hardness, 40 Rc+, encompassing hard metals or carbides.
In certain wear applications, e.g., exploration wells in crude oil or natural gas fields such as directional bores and the like, it is advantageous for drilling string components including drill stems to be made of materials with magnetic permeability values below about 1.02 or possibly even less than 1.01 (API Specification 7 regarding drill string components), in order to be able to follow the exact position of the bore hole and to ascertain and correct deviations from its projected course.
A number of other disclosures are directed to non-magnetic alloys for use in forming drilling components including U.S. Pat. No. 4,919,728 which details a method for manufacturing non-magnetic drilling string components. US Patent Publication No. 2005/0047952 describes a non-magnetic corrosion resistant high strength steel. Although both patents describe magnetic permeability of less than 1.01, the compositions described have a maximum of 0.15 wt % carbon, 1 wt % silicon and no boron. The low levels and absence of the above mentioned hard particle forming elements suggests that the alloys would not precipitate sufficient, if any, hard particles. It can be further expected that inadequate wear resistance and hardness for high wear environments would be provided. U.S. Pat. No. 4,919,728 describes alloys which contain carbon levels below 0.25 wt % while US Patent Publication No. 2005/0047952 details carbon levels below 0.1 wt %, significantly below the alloys discussed in this disclosure. With these levels of carbon in conjunction with the absence of boron, few hard particles can form which impart wear resistance to a hardband. Also in U.S. Pat. No. 4,919,728, a method for cold working at various temperatures is used to achieve the desired properties. Cold working is not possible in coating applications such as hardfacing. The size and geometry of the parts would require excessive deformations loads as well as currently unknown methods to uniformly cold work specialized parts such as tool joints.
US Patent Publication No. 2010/0009089 details a non-magnetic for coatings adapted for high wear applications where non-magnetic properties are required. The alloys listed in this publication are nickel-based with preformed tungsten carbide hard spherical particles poured into the molten weld material during welding in the amount of 30-60 wt %.
Disclosures offering alloying solutions for competing wear mechanisms in oil & gas drilling hardfacing applications include but are not limited to U.S. Pat. Nos. 4,277,108; 4,666,797; 6,117,493; 6,326,582; 6,582,126; 7,219,727; and US Patent Publication No. 2002/0054972. US Publication Nos. 2011/0220415 and 2011/0042069 disclose an ultra-low friction coating for drill stem assemblies. U.S. Pat. Nos. 6,375,895, 7,361,411, 7,569,286, 20040206726, 20080241584, and 2011/0100720 disclose the use of hard alloys for the competing wear mechanisms.
There is still a need for non-magnetic alloy compositions for hardbanding components for use in directional drilling applications that have resistance to abrasion. There is also a need for an improved method to protect drill collars from heavy abrasion during drilling operations.
The austenite phase described as a component of this disclosure is naturally paramagnetic while ferrite which composes typical hardbanding is ferromagnetic. When a magnet is brought into close proximity or contact with a ferromagnetic hardband, it exhibits attractive forces. A magnet exhibits no detectable attraction to an entirely austenitic material.
Magnetic permeability is the measure of how well a material can support a magnetic field within it. The relative magnetic permeability of a vacuum is 1. The definition of a non-magnetic material suitable for use on a drill collar is <1.01 according to API Specification 7. Even slight amounts of ferrite or martensite in a mainly austenitic material can cause the magnetic permeability to exceed 1.01. Ferrite and martensite have a magnetic permeability greater than 50 depending on the alloy composition. The magnetic permeability of magnetic hardbanding materials is not readily available because it is generally not of concern in applications where they are used. However, it can be inferred that the magnetic permeability will be similar to that of traditional magnetic materials such as alloy steels.
According to API Specification 7, a non-magnetic material for use on drill collars must maintain a magnetic field gradient of ±0.05. The magnetic field gradient is a measure of the uniformity of the magnetic field.